SHENYANG, Jan. 22 (Xinhua) -- Archaeologists found a sophisticated drainage system in an ancient noble tomb cluster in northeast China's Liaoning Province, local archaeological authorities said Tuesday.

The provincial cultural relics and archaeological institute said that a tomb group dating back to the Liao Dynasty (916-1125) was discovered in Xinli Village in the city of Jinzhou.

The excavation work started after the local archaeological department received the green light from the National Cultural Heritage Administration in May 2017.

Archaeologists unearthed five brick-chambered tombs, which had been raided several times and badly damaged. A series of utensils, including ceramics, metalware, jadeware, stoneware, glassware, amber accessories and tomb inscriptions have been found.

Wall paintings depicting carriages, horses, people and camels have also been discovered in the tomb tunnel and a chamber.

"One of the most unique findings was a relatively advanced drainage system," said Si Weiwei, a researcher of the provincial cultural relics and archaeological institute.

"Water in the tombs can be removed through the drainage ditches," Si said, adding that the drainage system was 110-meter-long and stone balls were paved below the ditches.

Si said that flagstones were laid around 60 centimeters above the stone balls and were covered by bricks. Water in the tombs flowed from the space between the stone balls.

The stone balls aimed to drain and prevent tomb raiders, according to experts.

Documents and inscriptions unearthed in the tombs indicated that it was a family graveyard of the nobility of the Khitan tribes, who founded the Liao Dynasty and once ruled the northern part of China.